Progressive-burning smokeless powder



Patented Nov. 7, 1939 rear orrles PROGRESSIVE-BURNING SMOKELESS POWDERElton R. Allison, Kenvil, N. J., assignor to Hercules Powder Company,Wilmington, Del, a corporation of Delaware No Drawing. ApplicationOctober 6, 1938, Serial No. 233,596

7 Claims.

This invention relates to smokeless powder, and particularly to coated,deterred, or progressive-burning smokeless powder.

Smokeless powder, on combustion in the chamher of the gun in which it isused, tends to burn initially at a more rapid rate than is desired andthus produces high breech pressures. This defeet is not overcome byusing larger grains of powder, in the case of those powders intended togive maximum results in center-fire rifle cartridges. Many attempts havebeen made in the past to deter the initial rate of burning of the powdergrains by coating said grains with an agent, explosive or non-explosive,which will slow down the initial rate of combustion of the powdergrains, thus extending the period of time taken by the grains to burncompletely, and in this way reduce the otherwise high breech pressure inthe The coating material used penetrates the 530 powder grains more orless, so that, as the powder grains burn, the successively exposedsurfaces contain, gradually, less and less of the deterrent material,thus causing subsequent combustion of the powder grain to proceed withincreasing .3 speed as the bullet travels down the bore of the gun.

In .the past, many substances have been used, without complete success,to coat smokeless powder grains, e. g., such materials as diethyldiphenaylurea, dimethyldiphenylurea, dinitrotoluene, a1-

k'yl phthalates, or mixtures thereof, and various methods of applyingsuch deterrent substances have been known.

The known methods of deterring or coating ,3; smokeless powders have notbeen completely effective in that they have not produced smokelesspowders of high gravimetric density combined with high ballisticstability. By ballistic stability is meant the maintenance, with age, ofthe inw :tial ballistics produced by the powder. For example, many ofthe coating agents continue to penetrate into the powder grain,particularly in warm climates, and thus alter their deterrentcharacteristics.

A; With modern loads of deterred smokeless powstable with age and ofhigh gravimetric (or loading) density. The high gravimetric density ofmy coated powders enables me to use greater charges than hithertopermitted by the volumetric capacity of the cartridge, which is a dis--5 tinct improvement over prior art powders and an advantage which hasbeen sought for many years by the art. In addition my improved smokelesspowder is not subject to clustering or sticking together of the grains.101

In the preparation of coated smokeless powder in accordance with myinvention, I use as coating agents the aryl esters of benzoic acid orthe aryl esters of a lower fatty acid which are characterized by havinga melting point within the '15} range from about 35 C. to about 110 C.Among these compounds which I have found suitable as coating agents arephenyl benzoate, naphthyl benzoate, A-naphthyl acetate, B-naphthylacetate, B-naphthyl prop-ionate, and B-naphthyl isobutyrate. Thesmokeless powder may be coated with any of these compounds alone or withvarious combinations of these compounds or these compounds may be usedin combination with other coating agents.

I may use as the powder grain to be coated either a single base(nitrocellulose) powder, or a double base (nitrocellulose-nitroglycerin)powder. Although the powder grain may be of any size, I have found thatmy coating agents offer the most advantage when used with the largercaliber powders.

In practicing my invention the herein specified coating agents areapplied to the smokeless powder as a solution ofsaid coating agents in a.35 volatile solvent which is substantially a nonsolvent for thesmokeless powder. Among the volatile solvents which I have used aretoluene, ethylene dichloride, petroleum naphtha, isopropyl alcohol andethyl alcohol and of these I prefer using 95% by volume ethyl alcohol.To 100 parts by weight of smokeless powder I add from about 1 to about10 parts by weight of the specified coating agents, dissolved in asuitable quantity of solvent. The smokeless powder is treated with thecoating agent in any suitable manner, for example, by tumbling thepowder and the coating agent solution in a barrel at a temperaturewithin the range from about 10 C. to about 95 C. for a period of timebetween about 5 minutes to about 4 hours, after which the powder socoated may be subjected to further heat treatment to eliminate anyremaining solvent, if this appears desirable. The time and temperatureof treatment, as well as the quantity of coating As specificillustrations of the carrying out of my invention, the followingexamples are given: Example 1 Nine hundred and seven parts by weight ofa double base smokeless powder containing 20% nitroglycerine, pressedthrough a 0.045 inch die having a 0.015 inch pin, and the strand soproduced' cut into 11 particles per inch, was placed in a sweetie barrelmaintained at 75 C., and to this was added 45.3 parts by weight ofphenyl benzoate dissolved in 160 parts by weight of ethyl alcohol. Themixture was tumbled in the closed sweetie barrel for hour at 75 C., thenfor another hour at 90 C., after which time the powder was removed to adry house and dried for three days at 55 C., then graphited, screenedand exposed to an atmosphere of 50% to 60% relative humidity to bringthe moisture content to equilibrium. A yield of 94% of unclusteredpowder was obtained having a gravimetric density of 0.951.

Example 2 Nine hundred and seven parts by weight of the same smokelesspowder as in the preceding example was coated in the same manner as inExample 1 with 45.3 parts by weight of B- naphthyl acetate dissolved in160 parts by weight of ethyl alcohol and then finished in the samemanner indicated in Example 1. A yield of 97% of unclustered powder wasobtained having a gravimetric density of 0.940.

I Ezrample 3 As a comparison with the above examples, I coated 907 partsby weight of the same smokeless powder as above in the same manner asalready indicated with 45.3 parts by weight of symmetricaldiethyldiphenylurea (Centralite #1). A yield of 68% of unclusteredpowder was obtained having a low and unsatisfactory gravimetric densityof 0.919.

Powders prepared in accordance with the three examples above were firedin a .30 caliber-1906 cartridge case using a 110 grain bullet, thecartridge being loaded in each case with sufficient powder to fill saidcartridge to the base of the It will be noted in the above table thatpowders coated with the agents disclosed by the present invention havean appreciable velocity increase over comparator Example 3 in which aprior art coating material is used. Furthermore, in comparison withExample 3 it will be noted that a greater charge of powder can beutilized in the same space in the cartridge in the case of Examples 1and 2 which is, of course, due to the higher gravimetric densities ofpowders prepared in accordance with this invention.

To illustrate the improvement in stability obtained by my coatedpowders, I subjected some of these to warm storage using for comparisona powder coated in the same manner with butylphthalyl butylglycollate.These results are shown in the following table:

The improvement in ballistic stability is apparent from the above table.

It will be understood that the foregoing examples are by way ofillustration only, and that the scope of my invention is not to belimited thereto, except as hereinafter defined by the claims.

What I claim and desire to protect by Letters Patent is:

1. Smokeless powder grains surface coated with an aryl ester of anorganic acid selected from the group consisting of benzoic acid and alower fatty acid, said ester being characterized by having a meltingpoint within the range from about 35 C. to about 110 C.

2. Smokeless powder grains surface coated with about 1% to about byweight of an aryl ester of an organic acid selected from the groupconsisting of benzoic acid and a lower fatty acid, said ester beingcharacterized by having a melting point within the range from about 35C. to about 110 C.

3. Smokeless power grains surface coated with phenyl benzoate.

4. Smokeless powder grains surface coated with B-naphthyl acetate.

5. Double base smokeless powder grains surface coated with an aryl esterof an organic acid selected from the group consisting of benzoic acidand a lower fatty acid, said ester being characterized by having amelting point within the range from about 35 C. to about 110 C.

6. Double base smokeless powder grains surface coated with phenylbenzoate.

'7. Double base smokeless powder grains surface coated with B-naphthylacetate.

ELTON R. ALLISON.

